The present invention relates to a vehicle air conditioner to be mounted on a vehicle, and more particularly relates to an air conditioner with a heat pump device.
An air conditioner with a heat pump device has been known in the art as an air conditioner to be mounted on hybrid vehicles, electric vehicles and other kinds of vehicles. A heat pump device for use in each of those vehicles is formed by connecting together an electric compressor, an exterior heat exchanger provided outside the vehicle cabin, a pressure reducing valve, and an interior heat exchanger provided inside the vehicle cabin in this order via refrigerant piping (see, for example, Japanese Unexamined Patent Publication No. 2011-5983).
When the heat pump device operates in a heating operation mode, the refrigerant is allowed to flow so that the interior heat exchanger functions as a radiator and the exterior heat exchanger functions as a heat absorber. On the other hand, when the heat pump device operates in a cooling operation mode, the refrigerant is allowed to flow so that the interior heat exchanger functions as a heat absorber and the exterior heat exchanger functions as a radiator.
Meanwhile, a vehicle air conditioner as disclosed in Japanese Unexamined Patent Publication No. 2011-255735, for example, includes an upstream interior heat exchanger provided upstream in the airflow direction and a downstream interior heat exchanger provided downstream in that direction. Its refrigerant piping includes a four-way valve. By turning this four-way valve, a switch is made between multiple operation modes such as a heating operation mode and a cooling operation mode.
As another example, a vehicle air conditioner as disclosed in Japanese Unexamined Patent Publication No. H09-240266 includes, as interior heat exchangers, an upstream interior heat exchanger provided upstream in the airflow direction and a downstream interior heat exchanger provided downstream in that direction. The downstream interior heat exchanger functions as a radiator in both of heating and cooling operation modes, while the upstream interior heat exchanger functions as a heat absorber in both of the heating and cooling operation modes.
Considering various possible situations in which the vehicle cabin needs to be air-conditioned, a so-called “dehumidification and heating operation” of heating the vehicle cabin while decreasing the humidity thereof sometimes needs to be performed. When the dehumidification and heating operation is performed, however, the interior environment may vary depending on some external factor. For example, if the humidity is low (e.g., when the outdoor air temperature is low), only a low dehumidifying capacity is needed. On the other hand, if the humidity is high (e.g., when the outdoor air temperature is relatively high), a high dehumidifying capacity is needed. Since the dehumidifying capacity is controllable by adjusting the pressure and temperature of the refrigerant supplied to the interior heat exchanger, a low-temperature refrigerant may be supplied to the interior heat exchanger to achieve a high dehumidifying capacity.
Nevertheless, while the dehumidification and heating operation is performed, a heating capacity is required. That is why a sufficiently high heating capacity could not be achieved simply by supplying a low-temperature refrigerant uniformly to the interior heat exchanger in order to increase the dehumidifying capacity.
In view of the foregoing background, it is therefore an object of the present invention to allow for controlling the dehumidifying capacity appropriately while achieving a sufficiently high heating capacity during the dehumidification and heating operation.
Also, while the dehumidification and heating operation is performed, the condensate in the interior heat exchanger gets frozen to cause frosting there. Once frosting has occurred, the interior heat exchanger is no longer able to exchange heat, and therefore, a frost reducing operation needs to be performed. However, the frosting reducing operation may sometimes make the occupant uncomfortable. That is why if the dehumidification and heating operation mode needs to be switched between multiple modes as described above, people want to perform the frost reducing operation efficiently in each of those operation modes.
It is therefore another object of the present invention to allow for performing the frost reducing operation efficiently when the heat pump device is operated at a dehumidifying capacity corresponding to the required degree of dehumidification.